Provide a way to tune the deferred wakeup level we want to perform from a safe wakeup point. Currently those sites are:
* nocb_timer * user/idle/guest entry * CPU down * softirq/rcuc
All of these sites perform the wake up for both RCU_NOCB_WAKE and RCU_NOCB_WAKE_FORCE.
In order to merge nocb_timer and nocb_bypass_timer together, we plan to add a new RCU_NOCB_WAKE_BYPASS that really want to be deferred until a timer fires so that we don't wake up the NOCB-gp kthread too early.
To prepare for that, integrate a wake up level/limit that a callsite is deemed to perform.
Signed-off-by: Frederic Weisbecker frederic@kernel.org Cc: Josh Triplett josh@joshtriplett.org Cc: Lai Jiangshan jiangshanlai@gmail.com Cc: Joel Fernandes joel@joelfernandes.org Cc: Neeraj Upadhyay neeraju@codeaurora.org Cc: Boqun Feng boqun.feng@gmail.com --- kernel/rcu/tree.c | 2 +- kernel/rcu/tree.h | 2 +- kernel/rcu/tree_plugin.h | 15 ++++++++------- 3 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f74a9ba62c12..e31b1d8fde93 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3813,7 +3813,7 @@ static int rcu_pending(int user) check_cpu_stall(rdp);
/* Does this CPU need a deferred NOCB wakeup? */ - if (rcu_nocb_need_deferred_wakeup(rdp)) + if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE)) return 1;
/* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */ diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index b280a843bd2c..2510e86265c1 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -433,7 +433,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, bool *was_alldone, unsigned long flags); static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, unsigned long flags); -static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp); +static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level); static bool do_nocb_deferred_wakeup(struct rcu_data *rdp); static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp); static void rcu_spawn_cpu_nocb_kthread(int cpu); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index b1f76f341c66..162dda3714f1 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2354,13 +2354,14 @@ static int rcu_nocb_cb_kthread(void *arg) }
/* Is a deferred wakeup of rcu_nocb_kthread() required? */ -static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) +static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level) { - return READ_ONCE(rdp->nocb_defer_wakeup) > RCU_NOCB_WAKE_NOT; + return READ_ONCE(rdp->nocb_defer_wakeup) >= level; }
/* Do a deferred wakeup of rcu_nocb_kthread(). */ -static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp) +static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp, + int level) { unsigned long flags; int ndw; @@ -2369,7 +2370,7 @@ static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
- if (!rcu_nocb_need_deferred_wakeup(rdp_gp)) { + if (!rcu_nocb_need_deferred_wakeup(rdp_gp, level)) { raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);; return false; } @@ -2385,7 +2386,7 @@ static void do_nocb_deferred_wakeup_timer(struct timer_list *t) { struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
- do_nocb_deferred_wakeup_common(rdp); + do_nocb_deferred_wakeup_common(rdp, RCU_NOCB_WAKE); }
/* @@ -2398,8 +2399,8 @@ static bool do_nocb_deferred_wakeup(struct rcu_data *rdp) if (!rdp->nocb_gp_rdp) return false;
- if (rcu_nocb_need_deferred_wakeup(rdp->nocb_gp_rdp)) - return do_nocb_deferred_wakeup_common(rdp); + if (rcu_nocb_need_deferred_wakeup(rdp->nocb_gp_rdp, RCU_NOCB_WAKE)) + return do_nocb_deferred_wakeup_common(rdp, RCU_NOCB_WAKE); return false; }